Particle comprising a matrix and a radical initiator

ABSTRACT

The invention pertains to a particle comprising a composition containing a matrix and a peroxide or azo radical initiator, wherein the particle is a fiber or fibrid selected from aramid, polyester, polyimide, cellulose, and glass. The invention further relates to particle-elastomers comprising said composition, and skim products, tires, tire treads, and belts comprising these particle-elastomers.

The invention pertains to a particle comprising a composition containing a matrix and a peroxide or azo radical initiator. The invention further relates to a particle elastomer composition, and to a skim product, a tire, a tire tread, an undertread, a belt, and a hose comprising said particle-elastomer composition.

In the tire and belt industry, among others, better mechanical, heat build up and hysteresis properties are being demanded. It has long been known that the mechanical properties of rubber can be improved by using a large amount of sulfur as a cross-linking agent to increase the crosslink density in vulcanized rubbers. However, the use of large amounts of sulfur suffers from the disadvantage of high heat generation that leads to a marked decrease in heat resistance and resistance to flex cracking, among other properties, in the final product. In order to eliminate the foregoing disadvantage, it was proposed to add treated chopped fiber, pellets made thereof or treated pellets, particularly treated with polysulfides, Bunte salt, and sulfur to sulfur-vulcanization systems. These pellets further contain wax to improve processing. Although there were improvements in e.g. hysteresis and flex cracking, these improvements were not found when uncured compounds were aged before vulcanization. This is a drawback in applications where uncured compounds are kept for a certain number of days. The present invention has among others to its object to provide particles that maintain their advantageous properties when used in uncured compounds.

Waxed pellets as such are known in the art. For instance, in EP 0 889 072 the coating of aramid pellets with a polymeric component, e.g. a wax, was disclosed. However, these pellets do not comprise a peroxide- or an azo-containing wax.

In U.S. Pat. No. 6,068,922 pellets comprising aramid fibers and an extrudable polymer, e.g. polyethylene, polypropylene or polyamides are disclosed. The fibers may be coated by typical sizing agents (RF, epoxy, silicone). Coatings containing radical initiators are not disclosed.

The present invention provides a solution to the above problems which are associated with aging of unvulcanized compounds. Moreover, the particles of the invention provide further improvements of dynamic properties by using a novel class of treated particles, including chopped fibers, staple fiber, and pulp, in the sulfur and peroxide vulcanization of rubbers and provides in a particle that solves a long-standing problem of reducing hysteresis and heat generation in rubber compositions.

To this end the invention relates to a particle comprising a composition containing a matrix and a peroxide or azo radical initiator wherein the particle is a fiber or fibrid selected from aramid, polyester, polyamide, cellulose, and glass.

The peroxide can be any peroxide and contains at least one peroxide group. Peroxides can be either mono- or bisperoxides. Peroxides can be technically pure or mixed with an inorganic support such as clay or silica, a polymeric support such as EPDM or combinations of these supports. Furthermore, peroxides can be diluted with a solvent or an oil such as a paraffin oil. Furthermore, peroxides can be dispersed in silicone oil.

Examples of suitable peroxides include cyclic peroxide, diacyl peroxide, dialkyl peroxide, hydroperoxide, peroxycarbonate, peroxydicarbonate, peroxyester, ketone peroxide, derivatives of ketone peroxide, inorganic peroxide, peroxyketal, mixed peroxide and mixtures of any two or more of these peroxides. More preferably, the peroxide is selected from dialkyl peroxyketal, dialkyl peroxide, di(alkylperoxy)alkylene, di(alkylperoxy)aralkylene, alkyl acyl peroxide, alkyl hydro-peroxide, or a mixture thereof, such as dicumyl peroxide, di(tert-butyl)peroxide, di(tert-butylperoxyisopropyl)benzene, t-butyl peroxy-3,5,5-trimethylhexanoate, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, cumyl hydroperoxide, 1,1-(tert-butyl-peroxy)cyclohexane and 1,1-(tert-butylperoxy)-3,3,5-trimethylcyclohexane. Most preferably, the peroxide is 1,1-(tert-butylperoxy)cyclohexane or 1,1-(tert-butyl-peroxy)-3,3,5-trimethylcyclohexane.

Azo radical initiators have the general formula R—N═N—R′, which compounds can be a precursor of two carbon-centered radicals R▪ and R′▪ and nitrogen gas upon heating or irradiation. Azo radical initiators include compounds such as 2,2′-azobis(2-methylpropanenitrile), 1,1′-azobis(1-cyclohexanenitrile), 2,2′-azobis(2-methylbutanenitrile), 4,4′-azobis(4-cyanovaleric acid), 2,2′-azobis(methyl 2-methylpropanate), and 2,2′-azobis(2-phenylpropane).

In a preferred embodiment the invention relates to a particle comprising a matrix and a radical initiator, which enhances the rubber properties of an elastomer. The matrix may be a wax, an extrudable polymer, an inorganic filler, an oil, an organic solvent or a combination of two or more of these. The preferred composition contains up to 85 wt % of matrix, preferably wax and/or extrudable polymer, based on the weight of the composition. Examples of suitable waxes are microcrystalline wax of higher alkyl chains, such as a C22-C38 alkyl chain, paraffin wax or alkyl long chain fatty acid ester waxes, such as C12-C50 alkanecarboxylic acids esters. Instead of a wax, the matrix can also be selected from an extrudable polymer. Particularly useful are polyolefins, e.g. polyethylene, polypropylene or derivatives thereof, as well as mixtures thereof. The term “derivative” means that the polyolefin may be obtained from a certain olefin and minor amounts of other olefins, or that the polyolefin is a grafted polyolefin. For example, instead of pure polyethylene also modified polyethylene such as Plexar® can be used. Polyolefins include high and low density polymers and copolymers. Polyamides can also be used. The extrudable polymer can also be used as a mixture with a wax. The matrix can contain one or more inorganic fillers, such as silica, whiting and clay. The matrix can contain oil, such as paraffin or naphthene oils. Optionally, the matrix can contain a solvent, such as a saturated alkane.

The peroxide initiator and/or the azo initiator as present in the composition do not have any measurable effect on the vulcanization of the rubber. The content of this initiator in the composition is far too low to effectively vulcanize rubber. Thus independently from the radical initiator in the composition of this invention it is necessary to use peroxide or sulfur to vulcanize the rubber. The radical initiator in the particle comprising the composition thus is believed to have only a substantial and advantageous effect on the adhesion of the particles to the rubber. It is further believed that this improved adhesion is responsible for the improved properties, such as modulus, hardness, abrasion resistance, hysteresis, Payne effect, and heat build-up of rubbers thus treated.

The term “particle” as used herein relates to any shape of a particle, including a pellet as obtained by compressing individual particles by conventional means. The particles may be provided with the composition, and pellets can be made thereof, for instance by cutting the particle contained in the matrix-radical initiator composition to pellets, or alternatively, first shaping the particles without composition into a pellet followed by treatment thereof with the composition. The pellet may be composed of any particle according to the invention. Particles are selected from aramid, polyester, polyamide, cellulose, and glass. The particles are in the form of fiber or fibrid. Fibers include continuous fiber, chopped fiber, staple fiber, pulp or fibril. Fibrids are small, non-granular, non-rigid fibrous or film-like particles, wherein in films one of their dimensions is in the order of microns, and in fibers two dimensions are in the micron range. The term “fibrid” is well known in the art and clear to those skilled in the art. The skilled reader is further referred to U.S. Pat. No. 2,999,788 wherein a precise definition is given in which the term “fibrids” is further defined in that a fibrid particle must possess an ability to form a waterleaf. Aramid fibers (which include continuous fiber, chopped fiber, staple fiber, and pulp, which may be pre-treated with a sizing) have the preference, more specifically particles of poly(p-phenylene-terephthalamide) or co-poly-(paraphenylene/3,4′-oxydiphenylene terephthalamide. Most preferred are chopped fiber and staple fiber.

The term “pellet” includes terms, apart from pellet, that are synonymous or closely related such as tablet, briquette, pastilles, granule and the like.

Pellets can be made from short cut fibers, chopped fiber, staple fiber, pulp, fibrils, and fibrid by mixing these particles with the radical initiator and a matrix, such as a matrix of a wax, an extrudable polymer, an inorganic filler, an oil, a solvent and/or any suitable combination of these.

For instance, the pellet can be prepared according to the method described in WO 0058064. Alternatively, pellets can be prepared directly using chopped fiber and the like, wax, and the radical initiator. The particles, the matrix, and the radical initiator are mixed intensively and optionally heated up to a temperature at or above the melting point of the wax or extruded polymer. Then the mixture is formed into the shape of a pellet at a temperature below the melting point of the wax or extruded polymer. Wax (and/or extrudable polymer) can be used in amounts up to 85 wt % based upon the weight of the particle together with the composition. Alternatively, pellets can also be made from a mixture of particle and matrix, after which the radical initiator is added.

A particularly preferred embodiment of the invention is particles provided with the composition in the form of a coating. Such particles, most preferably shaped into a pellet, are then at least partially coated with the composition or particles already provided with a matrix are at least partially coated with the radical initiator. Coating of the particles, for instance, can be carried out using a solution of radical initiator in a suitable solvent, e.g. toluene or using a dispersion of said radical initiator in e.g. toluene/water.

The meaning of the term “coating” is well known for the skilled man and can be found in any relevant textbook. Thus a coated particle is a particle containing a layer of the coating material (the coating) around its surface. If the particle is partially coated, only part of the particle is covered by said layer. In principle there is no difference whether the particles are coated and made to a pellet, or when the particles are made to a pellet and then coated. The coating composition will completely penetrate the pellet and coat the individual particles therein. It is also possible that the coating material or part of the coating material penetrates between fibers of the particle, or even between filaments and microfilaments, thereby impregnating the particle.

The treatment of the particle thereof is based on the above radical initiator, preferably selected from 1,1-(tent-butylperoxy)cyclohexane and 1,1-(tert-butyl-peroxy)-3,3,5-trimethylcyclohexane.

The treatment of the particle (or the particle being shaped into a pellet) is based on the above matrix such as paraffin wax, and peroxide and/or azo radical initiator. It should be stressed that the at least partial coating of the particle can be done on the particle as such, or on the particle after pelletization of the particle.

Particles of the invention can also contain a wax as a carrier medium to improve processing. Examples of suitable waxes are microcrystalline wax of higher alkyl chains, such as C22-C38 alkyl chains, paraffin wax, or alkyl long chain fatty acid ester waxes, such as C12-C50 alkanecarboxylic acids esters. After treatment the particle may be used as such or may be comminuted to appropriate size, to be suitably used in rubber compounds, After treatment fibers may be chopped to appropriate length, for use in rubber compounds, or chopped fiber may be treated by the above chemicals, or chopped fibers and the above chemicals including a wax may be mixed, optionally heated and formed into a well dosable shape.

The radical initiator amounts 0.5 to 50 wt %, preferably 1 to 30 wt %, more preferably 2 to 20 wt %, based on the weight of the particle. Throughout this description the expression “based on the weight of the particle” means based on the total weight of the particle provided with the composition.

Pellets prepared according to the method described in WO 0058064 can be treated either using a solution of radical initiator in a suitable solvent e.g. toluene or a dispersion of said radical initiator in e.g. toluene/water or using a mixture of said radical initiator in a suitable matrix such as stearyl or palmityl stearate. The matrix preferably comprises up to 85 wt % of the particle, more preferably between 20 and 67 wt %.

Pellets can be prepared directly using chopped fiber, wax, and radical initiator as described above. Preferably, the wax is stearyl stearate or palmityl stearate.

Preferred compositions comprise 5-98 wt % radical initiator based on the weight of the composition. The expression “the weight of the composition” as used in this description means the weight of the composition only, i.e. without the particle.

In another aspect the invention relates to an uncured rubber composition obtained by mixing the elastomer, the particle of the invention, the filler and optionally other rubber additives in absence of the vulcanization agents.

The mixing process is carried out with the elastomer in the presence of 0.1 to 20 phr, more preferable of 0.5-10 phr of the particle according to the invention at a temperature in the range from 110 to 220° C. for a period of up to 2 hours. Preferably, the mixing temperature is chosen to obtain good incorporation of the particle of the invention and thereby obtaining significant reduction of the Payne effect and hysteresis within 5 minutes of mixing. Preferably, the particle of the invention is added together with the filler. The mixing process can be carried out in any mixer in which the uncured rubber composition can be mixed and can be heated to the required temperature. Preferably, the mixing is carried out in an internal mixer such as a Banbury mixer.

The expression “uncured elastomeric product” is defined as that less than 10 wt %, preferably less than 5 wt %, and even more preferably less than 1 wt % of the elastomer is cured. Most preferred the amount of the particle of the invention is low enough to prevent any curing of the elastomer product.

In another aspect the invention relates to a rubber composition which is the vulcanization reaction product of the above uncured rubber composition comprising the particle according to the invention, and a vulcanization agent. The particle of the invention lowers hysteresis and the Payne effect and reduces the heat build-up of the rubber composition. Also disclosed is a vulcanization process carried out in the presence of the uncured elastomer product comprising the particle of the invention and the use of these particles in the vulcanization of rubbers. The vulcanization agent can be either a peroxide or sulfur. The sulfur may be replaced by a sulfur donor.

In addition, the present invention relates to a vulcanization process carried out in the presence of the particles and the use of these particles in the vulcanization of rubbers. Further, the invention also encompasses rubber products which comprise at least some rubber which has been vulcanized, preferably vulcanized with sulfur or peroxide, in the presence of said particles.

The present invention provides rubber having excellent hysteresis behavior and heat build-up without having a significant adverse effect on the remaining properties, when compared with similar sulfur- or peroxide-vulcanization systems without any of the particles. Furthermore, rubber compound properties are independent of the time between mixing and vulcanization over a period of at least 28 days.

To this end, the invention also relates to an elastomer composition comprising

(a) 100 parts by weight of at least one natural or synthetic rubber; (b1) 0.1 to 25 parts by weight of an amount of sulfur and/or a sulfur donor; or (b2) 0.1 to 20 parts by weight of peroxide; and (c) 0.1 to 20 parts by weight of the hereinabove described particle.

Preferred amounts of sulfur, respectively sulfur donor are 1 to 20 parts by weight, more preferably 1 to 15 parts.

Preferred amounts of peroxide are 1 to 20 parts by weight, more preferably 1 to 15 parts.

Preferred amounts of the above particle are in the range 1 to 20 parts by weight

The present invention is applicable to all natural and synthetic rubbers. Examples of such rubbers include, but are not limited to, natural rubber, styrene-butadiene rubber, butadiene rubber, isoprene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, isoprene-isobutylene rubber, brominated isoprene-isobutylene rubber, chlorinated isoprene-isobutylene rubber, ethylene-propylene-diene ter-polymers, as well as combinations of two or more of these rubbers and combinations of one or more of these rubbers with other rubbers and/or thermoplastic compounds.

When sulfur vulcanization is applied the required level of sulfur during the vulcanization process is provided by sulfur, optionally together with sulfur donors, or sulfur donors only. Examples of sulfur which may be used in the vulcanization process include various types of sulfur such as powdered sulfur, precipitated sulfur, and insoluble sulfur. Examples of sulfur donors include, but are not limited to, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, dipentamethylene thiuram hexasulfide, dipentamethylene thiuram tetrasulfide, dithiodimorpholine, and mixtures thereof.

Sulfur donors may be used instead or in addition to the sulfur. Herein the term “sulfur” shall further also include sulfur donors and the mixture of sulfur and sulfur donor(s). Further, the quantity of sulfur employed in the vulcanization process when applied to sulfur donors, means the quantity of sulfur that is rendered by the sulfur donor.

More particularly, the present invention relates to a sulfur-vulcanized rubber composition which comprises the vulcanization reaction product of: (a) 100 parts by weight of at least one natural or synthetic rubber; (b) 0.1 to 25 parts by weight of an amount of sulfur and/or an amount of sulfur donor providing 0.1 to 25 parts by weight of sulfur; and (c) 0.1 to 20 parts by weight of the particle of the invention, preferably wherein the particle is chopped fiber, staple fiber, or pellets made thereof.

The particle of the present invention is based on natural and synthetic polymers. Examples of such polymers include aramid, such as para-aramid, polyimide, polyester, cellulose, such as rayon, and glass as well as combinations of two or more of these yarns.

Most preferably the particle is poly(para-phenylene-terephthalamide) fiber, which is commercially available under the trade name Twaron®, or co-poly-(para-phenylene/3,4′-oxydiphenylene terephthalamide), which is commercially available under the trade name Technora®.

The amount of sulfur to be compounded with the rubber is, based on 100 parts of rubber, usually 0.1 to 25 parts by weight, and more preferably 0.2 to 8 parts by weight. The amount of particle to be compounded with the rubber is, based on 100 parts of rubber, 0.1 to 25 parts by weight, and more preferably 0.2 to 10.0 parts by weight, and most preferably 0.5 to 5 parts by weight. The vulcanization agent and the particle of the invention may be added as a pre-mix, or simultaneously or separately to the rubber, and they may be added separately or together with other rubber compounding ingredients as well. Usually it is also desirable to have a vulcanization accelerator in the rubber compound. Conventional known vulcanization accelerators may be employed. Preferred vulcanization accelerators include mercapto benzothiazole, 2,2′-mercapto benzothiazole disulfide, sulfenamide accelerators including N-cyclohexyl-2-benzothiazole sulfenamide, N-tert-butyl-2-benzothiazole sulfenamide, dicyclohexyl-2-benzothiazole sulfenamide, and 2-(morpholinothio)benzothiazole; thiophosphoric acid derivative accelerators, thiurams, dithiocarbamates, diphenyl guanidine, diorthotolyl guanidine, dithiocarbamylsulfenamides, xanthates, triazine accelerators and mixtures thereof.

If the vulcanization accelerator is employed, quantities of from 0.1 to 8 parts by weight, based on 100 parts by weight of rubber composition, are used. More preferably, the vulcanization accelerator comprises 0.3 to 4.0 parts by weight, based on 100 parts by weight of rubber.

The vulcanization process can also be performed by non-sulfur containing compounds, such as peroxides or a combination of metal oxide and ethylene thiourea. Preferably, the non-sulfur vulcanization process is performed by peroxides. Examples of peroxides which may be used in the vulcanization process include various types of dialkyl, alkyl-aralkyl, diaralkyl, alkyl-ketal and diaroyl peroxide and mixtures thereof. Peroxides can be either mono- or bisperoxides. Examples of such peroxides include dicumyl peroxide, di(tert-butyl)peroxide, tert-butylcumylperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3, butyl 4,4-di(tert-butyl-peroxy)valerate and di(tert-butylperoxyisopropyl)benzene. Peroxides can be technically pure or mixed with an inorganic support such as clay or silica, a polymeric support such as EPDM or combinations of these supports. Peroxides can be dispersed in silicone oil.

Furthermore, the vulcanization process can be carried out in the presence of a polymerizable multifunctional monomer.

The amount of peroxide to be compounded with the rubber is, based on 100 parts of rubber, usually 1 to 20 parts by weight, and more preferably 2 to 12 parts by weight. The amount of the particle of the invention, preferably peroxide treated aramid particle or pellet, to be compounded with the rubber is, based on 100 parts of rubber, 0.1 to 20 parts by weight, and more preferably 0.5 to 15 parts by weight, and most preferably 1 to 10 parts by weight. These ingredients may be employed as a pre-mix, or added simultaneously or separately, and they may be added separately or together with other rubber compounding ingredients as well.

Other conventional rubber additives may also be employed in their usual amounts in both sulfur vulcanization and peroxide vulcanization. For example, reinforcing agent such as carbon black, silica, clay, whiting, and other mineral fillers, as well as mixtures of fillers, may be included in the rubber composition. Other additives such as process oils, tackifiers, waxes, antioxidants, antiozonants, pigments, resins, plasticizers, process aids, factice, compounding agents and activators such as stearic acid and zinc oxide may be included in conventional, known amounts. Rubber additives which may be used are well known to the skilled man and an extensive listing thereof can be found in textbooks such as W. Hofmann, “Rubber Technology Handbook, Chapter 4, Rubber Chemicals and Additives, pp. 217-353, Hanser Publishers, Munich 1989.

Further, scorch retarders such as phthalic anhydride, pyromellitic anhydride, benzene hexacarboxylic trianhydride, 4-methylphthalic anhydride, trimellitic anhydride, 4-chlorophthalic anhydride, N-cyclohexyl-thiophthalimide, salicylic acid, benzoic acid, maleic anhydride and N-nitrosodiphenylamine may also be included in the rubber composition in conventional, known amounts. Finally, in specific applications it may also be desirable to include steel-cord adhesion promoters such as cobalt salts and dithiosulfates in conventional quantities.

The process is carried out at a temperature of 110-220° C. over a period of up to 24 hours. More preferably, the process is carried out at a temperature of 120-190° C. over a period of up to 8 hours in the presence of 0.1 to 20 parts by weight, more preferable is the use of 0.2-5 parts by weight, of the particles of the invention, more specifically, comprising chopped fiber, staple fiber, or pellets made thereof. The additives to the rubber composition as mentioned above, may also be present during the vulcanization process.

In a more preferred embodiment the vulcanization process is carried out at a temperature of 120-190° C. for 8 hours or less in the presence of 0.1 to 8 parts by weight, based on 100 parts by weight of rubber, of at least one vulcanization accelerator.

The invention also includes articles of manufacture, such as skim products, tires, tire treads, tire undertreads, belts, or hoses which comprise sulfur- or peroxide-vulcanized rubber which is vulcanized in the presence of the particle of the present invention.

The invention is further illustrated by the following examples which are not to be construed as limiting the invention in any way.

Experimental Methods

In the following examples, rubber compounding, vulcanization and testing was carried out according to standard methods except as otherwise stated: Base compounds were mixed in a Farrel Bridge™ BR 1.6 liter Banbury type internal mixer (preheating at 50° C., rotor speed 77 rpm, mixing time 6 min with full cooling).

Vulcanization ingredients were added to the compounds on a Schwabenthan Polymix™ 150L two-roll mill (friction 1:1.22, temperature 70° C., 3 min).

Cure characteristics were determined using a Monsanto™ rheometer MDR 2000E (arc 0.5°) according to ISO 6502/1999. Delta S is defined as extent of crosslinking and is derived from subtraction of lowest torque (ML) from highest torque (MH).

Sheets and test specimens were vulcanized by compression molding in a Fontyne™ TP-400 press.

Tensile measurements were carried out using a Zwick™ 1445 tensile tester (ISO-2 dumbbells, tensile properties according to ASTM D 412-87, tear strength according to ASTM D 624-86).

Abrasion was determined using a Zwick abrasion tester as volume loss per 40 m path traveled (DIN 53516).

Hardness (IRHD) is measured according to ISO 48:1994.

Heat build-up and compression set after dynamic loading were determined using a Goodrich™ Flexometer (load 1 MPa, stroke 0.445 cm, frequency 30 Hz, start temperature 100° C., running time 120 min or till blow out; ASTM D 623-78). Dynamic mechanical analyses, for example loss modulus and tangent delta were carried out using an Eplexor™ Dynamic Mechanical Analyzer (pre-strain 2%, frequency 10 Hz, ASTM D 2231).

The Payne effect is a particular feature of the stress-strain behavior of rubber, especially rubber compounds containing fillers such as carbon black. The measurement is carried out under cyclic loading conditions, and is manifest as a dependence of the visco-elastic storage modulus on the amplitude of the applied strain.

EXAMPLE 1

Aramid staple pellets were prepared according to WO 0058064 and contained 80 wt % Twaron and 20 wt % polyethylene resin. The treatment of these pellets was done in the following way:

Trigonox® 29-C75 and Trigonox® 29-40B are commercially available from Akzo Nobel Polymer Chemicals. Trigonox® 29 is 1,1-bis(t-butylperoxy)-3,5,5-trimethyl-cyclohexane. Trigonox® 29-075 is a 75 wt % solution of 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane in a mineral solvent and Trigonox® 29-40B is a mixture of 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane with silica and whiting.

About 50 g of para-aramid pellets were mixed with molten wax containing Trigonox® 29-C75 or 40B in various concentrations and optionally clay. When Trigonox® 29-C75 was applied, part of the mineral solvent present in Trigonox® 29-C75 was allowed to evaporate. Subsequently, pellets were cooled using dry-ice and a small excess of solidified wax, possibly containing small amounts of Trigonox® 29, was removed by sieving. As a comparison one sample without any Trigonox® 29 was prepared. The p-aramid fiber pellets are summarized in Table 1.

TABLE 1 Aramid fiber and treatments. Particle:polymer:wax:Trigonox29:additive wt %:wt %:wt %:wt %:wt % Remark Entry Twaron:PE:stearic acid:—:Sunolite 37.9:9.5:42.0:—:10.6 comparison T1 Twaron:PE:Sunolite:C75:solvent 37.6:9.4:36.8:14.8:1.4 invention T2 Twaron:PE:Sunolite:C75:solvent 37.8:9.4:39.7:10.7:2.4 invention T3 Twaron:PE:Sunolite:C75:solvent 38.2:9.6:43.5:7.1:1.6 invention T4 Twaron:PE:Sunolite:C75:solvent 38.3:9.6:47.8:3.6:0.7 invention T5 Twaron:PE:Sas. 5998:C75:solvent 37.6:9.4:44.2:7.2:16 invention T6 Twaron:PE:Sas. 5998:C75:clay:solvent 36.4:9.1:33.1:7.4:12.5:1.5 invention 77 Twaron:PE:St. st.:C75:solvent 38.4:9.6:43.5:7.1:1.4 invention T8 Twaron:PE:Sunolite:40B:silica/whiting 33.0:8.2:24.7:13.7:20.6 invention T9 Twaron:PE:Sunolite:40B:silica/whiting 36.2:9.0:36.5:7.3:11.0 invention T10 PE = polyethylene; Sunolite = Sunolite 240, a microcrystalline wax; solvent = mineral spirit present in Trigonox ® 29-C75; Sas. 5998 = Sasolwax 5998, which is a paraffin wax; clay = Polestar 200 clay; St. st. = stearyl stearate (Radia ® 7501 from Oleon NV); silica/whiting = mixture of silica and whiting present in Trigonox 29-40B.

The accelerator employed was N-cyclohexyl-2-benzothiazole sulfenamide (CBS). Details of the formulations are given in Table 2.

TABLE 2 Rubber formulations incorporating aramid fiber particles Experiment Ingredients A B 1 2 3 4 5 6 7 8 9 10 NR SVR 10 80 80 80 80 80 80 80 80 80 80 80 80 Europrene BR 40 20 20 20 20 20 20 20 20 20 20 20 20 Black N-326 53 53 53 53 53 53 53 53 53 53 53 53 Zinc oxide 5 5 5 5 5 5 5 5 5 5 5 5 Stearic acid 2 2 0.72 2 2 2 2 2 2 2 2 2 Aromatic oil 8 8 8 8 8 8 8 8 8 8 8 8 Antidegradant 6PPD 2 2 2 2 2 2 2 2 2 2 2 2 Antioxidant TMQ 1 1 1 1 1 1 1 1 1 1 1 1 Accelerator CBS 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Trigonox ® 29-40B 0.5 0 0 0 0 0 0 0 0 0 0 0 T1 0 0 3 0 0 0 0 0 0 0 0 0 T2 0 0 0 3 0 0 0 0 0 0 0 0 T3 0 0 0 0 3 0 0 0 0 0 0 0 T4 0 0 0 0 0 3 0 0 0 0 0 0 T5 0 0 0 0 0 0 3 0 0 0 0 0 T6 0 0 0 0 0 0 0 3 0 0 0 0 T7 0 0 0 0 0 0 0 0 3 0 0 0 T8 0 0 0 0 0 0 0 0 0 3 0 0 T9 0 0 0 0 0 0 0 0 0 0 3 0 T10 0 0 0 0 0 0 0 0 0 0 0 3 NR is natural rubber; BR is polybutadiene; 6PPD is N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine, TMQ is polymerized 2,2,4-trimethyl-1,2-dihydoquinoline antioxidant, CBS is N-cyclohexyl benzothiazyl sulfenamide.

The vulcanized rubbers listed in Table 2 were tested according to ASTM/ISO norms as described under Experimental methods. A is a control experiment with addition of Trigonox® 29-40B and B is a control experiments (rubber only), 1 is a comparative experiment with aramid particles without radical initiator and 2 to 10 are experiments according to the invention. The results are given in Tables 3-6.

TABLE 3 Effect of the mixes at 100° C. on processing characteristics (Mooney viscosity). Experiment A B 1 2 3 4 5 6 7 8 9 10 ML(1 + 4), MU 39.9 40.2 41.8 40.5 41.4 39.7 38.9 40.6 39.7 38.9 40 41.1

The data of Table 3 show that the staple fiber particles according to the invention (mix 2 to 10) show low viscosity as evidenced from the ML (1+4) values.

TABLE 4 Effect of the mixes at 150° C. on delta torque. Experiment A B 1 2 3 4 5 6 7 8 9 10 Delta S, Nm 1.40 1.42 1.50 1.37 1.40 1.43 1.47 1.43 1.45 1.43 1.42 1.44

The data in Table 4 show that the particles according to the invention (2 to 10) do not influence the extent of crosslinking as demonstrated by delta S values.

TABLE 5 Evaluation of staple fibers particles in Payne effect Experiment A B 1 2 3 4 5 6 7 8 9 10 Δ(G′_(0.7)-G′₂₀) (kPa) 165 158 188 82 91 106 153 93 106 102 94 102 Δ(G′_(0.7)-G′₉₀) (kPa) 206 200 233 132 138 152 197 140 151 147 140 148

it is clear from the data depicted in Table 5 that the particles of the invention have a lower Payne effect.

TABLE 6 Evaluation of improvement in dynamic mechanical properties Experiment A B 1 2 3 4 5 6 7 8 9 10 Temperature rise, ° C. 14.9 14.9 15.4 13.1 12.8 14.2 15.1 12.7 13.3 13.9 13.4 13.5 Loss modulus, MPa 0.88 0.97 1.07 0.645 0.645 0.79 0.88 0.75 0.78 0.78 0.68 0.79 Tangent delta 0.165 0.175 0.176 0.123 0.122 0.142 0.154 0.135 0.140 0.141 0.125 0.140

It is noted that the particles containing peroxide (mix 2 to 10) show improved dynamic mechanical properties. The improvement is realized independently of wax type (mixes 4, 6, and 8), presence of clay (mix 6 and 7) and peroxide formulation (mix 2 and 9). Higher peroxide concentrations in the aramid fiber particle give larger improvements in tangent delta (mix 2 to 5, and mix 9 and 10).

EXAMPLE 2

Aramid staple fiber pellets were prepared according to WO 0058064 and contained 80 wt % Twaron and 20 wt % polyethylene resin. The treatment of the pellets was done in the following way:

Radia® 7501 (stearyl stearate) is commercially available from Oleon NV. To an 80 L Nauta mixer, 9.0 kg of stearyl stearate were added and molten and heated to about 70° C. Next, 9.0 kg of Trigonox® 29-40B were added in portions. Mixing was continued until a homogeneous mass was obtained. Then 12 kg of aramid staple fiber pellets were added and mixing was continued for about 30 min. Then the heating was switched off and the product was cooled by the addition of 10.7 kg of dry-ice pellets. Finally, the Nauta mixer was emptied. The product (T11 in Table 7) was tested as such. The particle Twaron polyethylene:stearyl stearate:Trigonox 29-40B ratio equals 32:8:30:30.

The accelerator employed was N-cyclohexyl-2-benzothiazole sulfenamide (CBS). Details of the formulations are given in Table 7.

TABLE 7 Rubber formulations incorporating aramid pellets Experiment Ingredients C D 11 12 13 14 NR SVR 10 80 80 80 80 80 80 Europrene BR 40 20 20 20 20 20 20 Carbon Black N-326 55 53 53 53 53 53 Zinc oxide 5 5 5 5 5 5 Stearic acid 2 2 2 0 2 0 Aromatic oil 8 8 8 8 8 8 Antidegradant 6PPD 2 2 2 2 2 2 Antioxidant TMQ 1 1 1 1 1 1 Accelerator CBS 1.5 1.5 1.5 1.5 1.5 1.5 sulfur 1.5 1.5 1.5 1.5 1.5 1.5 T11 0 0 1 0 0 0 T11 0 0 0 2 0 0 T11 0 0 0 0 3 0 T11 0 0 0 0 0 5 NR is natural rubber; BR is polybutadiene; 6PPD is N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine, TMQ is polymerized 2,2,4-trimethyl-1,2-dihydoquinoline antioxidant.

The vulcanized rubbers listed in Table 7 were tested according to ASTM/ISO norms. C and D are control experiments (rubber only) and 11 to 14 are experiments according to the invention. The results are given in Tables 8-12.

TABLE 8 Effect of the mixes at 100° C. on processing characteristics (Mooney viscosity). Experiment C D 11 12 13 14 ML(1 + 4), MU 39 39 38 42 38 45

The data of Table 8 show that the fiber particle according to the invention show low viscosity as evidenced from the ML (1+4) values.

TABLE 9 Effect of the mixes at 150° C. on delta torque. Experiment C D 11 12 13 14 Delta S, Nm 1.54 1.48 1.47 1.40 1.42 1.42

The data in Table 9 show that the fiber particles according to the invention do not show an effect on delta torque values.

TABLE 10 Evaluation of treated fibers for improvement in mechanical properties Experiment C D 11 12 13 14 Modulus, 300%, MPa 8.8 8.5 9.2 10.6 10.0 10.5 Hardness (IRHD) 62 62 61 61 61 62

It is clear from the data given in Table 10 that the peroxide containing fiber particle (mix 11 to 14) of the invention have similar modulus and hardness as the reference compounds.

TABLE 11 Evaluation of improvement in dynamic mechanical properties Experiment C D 11 12 13 14 Loss modulus, MPa 0.94 0.92 0.72 0.65 0.70 0.70 Tangent delta 0.162 0.164 0.136 0.123 0.128 0.129

It is noted that the fiber particles (mixes 11 to 14) show improved dynamic mechanical properties.

TABLE 12 Evaluation of treated fiber particle in Payne effect at 100° C. Experiment C D 11 12 13 14 Δ(G′_(0.7)-G′₂₀) (kPa) 228 181 135 89 98 125 Δ(G′_(0.7)-G′₉₀) (kPa) 272 225 180 140 144 181

It is noted that the peroxide containing fiber particles (mixes 11 to 14) show improved Payne effect indicating a better distribution of carbon black in the rubber.

EXAMPLE 3

Aramid staple fiber pellets were prepared according to WO 0058064 and contained 80 wt % Twaron and 20 wt % polyethylene resin. The treatment of the pellets was done in the following way:

About 50 g of para-aramid pellets were mixed with molten wax containing a radical initiator in order to obtain an active oxygen concentration of about 1% unless indicated otherwise. Subsequently, pellets were cooled using dry-ice and a small excess of solidified wax, possibly containing small amounts of radical initiator, was removed by sieving. The p-aramid fiber pellets are summarized in Table 13.

TABLE 13 Aramid staple fiber pellets. Particle:polymer:wax:radical initiator:additive wt %:wt %:wt %:wt %:wt % Remark Entry Twaron:PE:St. St.:Trigonox 29- 40.2:10.1:30.9:12.5:6.3 invention T12 C75:Sunpar 2280 Twaron:PE:St. St.:dicumyl peroxide 39.4:9.9:34.3:16.4:— invention T13 Twaron:PE:St. St.:di(t-butylperoxy- 39.8:9.9:39.7:10.6:— invention T14 isopropyl)benzene Twaron:PE:St. St.:dilauroyl peroxide 40.2:10:25.8:24:— invention T15 Twaron:PE:St. St.:t-butylperoxy-3,5,5-tri- 40.2:10.1:35.6:14.1:— invention T16 methylhexanoate Twaron:PE:St. St.:t-butylperoxybenzoate 40.1:10:38.1:11.8:— invention T17 Twaron:PE:St. St.:cumyl hydroperoxide (88%) 40:10:39.7:10.3:— invention T18 Twaron:PE:St. St.:azobis(isobutyronitrile) (AIBN) 41.3:10.3:36.3:12.1:— invention T19 PE = polyethylene; St. St. = stearyl stearate (Radia ® 7501 from Oleon NV); Uptake of AIBN in T19 was not complete.

The accelerator employed was N-cyclohexyl-2-benzothiazole sulfonamide (CBS). Details of the formulations are listed in Table 14.

TABLE 14 Rubber formulations incorporating aramid fiber particles Experiment Ingredients E F 15 16 17 18 19 20 21 22 NR SVR 10 80 80 80 80 80 80 80 80 80 80 Europrene BR 40 20 20 20 20 20 20 20 20 20 20 Black N-326 55 53 53 53 53 53 53 53 53 53 Zinc oxide 5 5 5 5 5 5 5 5 5 5 Stearic acid 2 2 2 2 2 2 2 2 2 2 Aromatic oil 8 8 8 8 8 8 8 8 8 8 Antidegradant 6PPD 2 2 2 2 2 2 2 2 2 2 Antioxidant TMQ 1 1 1 1 1 1 1 1 1 1 Accelerator CBS 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 T12 0 0 3 0 0 0 0 0 0 0 T13 0 0 0 3 0 0 0 0 0 0 T14 0 0 0 0 3 0 0 0 0 0 T15 0 0 0 0 0 3 0 0 0 0 T16 0 0 0 0 0 0 3 0 0 0 T17 0 0 0 0 0 0 0 3 0 0 T18 0 0 0 0 0 0 0 0 3 0 T19 0 0 0 0 0 0 0 0 0 3 NR is natural rubber; BR is polybutadiene; 6PPD is N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine; TMQ is polymerized 2,2,4-trimethyl-1,2-dihydroquinoline antioxidant; CBS is N-cyclohexyl benzothiazyl sulfenamide.

The vulcanized rubbers listed in Table 14 were tested according to ASTM/ISO norms. E and F are control experiments (rubber only), and 15 to 22 are experiments according to the invention. The results are given in Tables 1547.

TABLE 15 Effect of the mixes at 150° C. on delta torque. Experiment E F 15 16 17 18 19 20 21 22 Delta S, Nm 1.52 1.44 1.47 1.48 1.5 1.51 1.49 1.53 1.52 1.5

The data in Table 15 show that the particles according to the invention (mix 15 to 22) do not influence the extent of crosslinking as demonstrated by delta S values.

TABLE 16 Evaluation of improvement in dynamic mechanical properties Experiment E F 15 16 17 18 19 20 21 22 Loss modulus, MPa 1.11 1.0 0.87 0.83 0.90 1.02 0.89 0.97 0.85 0.98 Tangent delta 0.180 0.177 0.154 0.146 0.153 0.170 0.151 0.160 0.146 0.164

The data in Table 16 show that all particles, each containing a different radical initiator, give a decrease in tan delta. The effect is found both for peroxide type radical initiators (mix 15 to 21) and azo type radical initiator (mix 22). The decrease in tangent delta is most significant when alkoxy and/or hydroxy radicals are generated (mixes 15, 16, 17, 19, 21).

TABLE 17 Evaluation of treated fiber particle in Payne effect at 100° C. Experiment E F 15 16 17 18 19 20 21 22 Δ(G′_(0.7)-G′₂₀) (kPa) 226 183 135 124 151 181 132 144 124 170 Δ(G′_(0.7)-G′₉₀) (kPa) 271 226 177 168 196 225 175 186 164 215

It is noted that the radical containing fiber particles (mixes 15 to 22) show improved Payne effect indicating a better distribution of carbon black in the rubber.

EXAMPLE 4

The same aramid fiber particle as described in Example 2 was used. The accelerator employed was N-cyclohexyl-2-benzothiazole sulfonamide (CBS). Details of the formulations are listed in Table 18. The formulations are representative of an off-the-road tire compound.

TABLE 18 Rubber formulations incorporating aramid pellets Experiment Ingredients G 23 24 NR SVR 10 100 100 100 Carbon Black N-220 40 40 40 Zeosil 1165 20 20 20 Si-69 1.5 1.5 1.5 Aromatic oil 3 3 3 Zinc oxide 5 5 5 stearic acid 2 2 2 In.-Cum.harz B/85 3 3 3 Sunolite 240 1 0.7 0.4 DPG 1 1 1 Accelerator CBS 1.5 1.5 1.5 sulfur 1.5 1.5 1.5 T11 0 0 0 T11 0 1 0 T11 0 0 2 NR is natural rubber; Zeosil 1165 is high surface silica; Si-69 is bis(3-triethoxysilylpropyl)tetrasulfide; In.-Cum.harz B/85 is a coumarone-indene resin; Sunolite 240 is a microcrystalline wax, DPG is diphenylguanidine.

The vulcanized rubbers listed in Table 18 were tested according to ASTM/ISO norms. G is a control experiment (rubber only) and 23 and 24 are experiments according to the invention. The results are given in Tables 19 to 23.

TABLE 19 Effect of the mixes at 100° C. on processing characteristics (Mooney viscosity). Experiment G 23 24 ML(1 + 4), MU 53 51 48

The data of Table 19 show that the staple fiber particle according to the invention show low viscosity as evidenced from the ML (1+4) values.

TABLE 20 Effect of the mixes at 150° C. on delta torque. Experiment G 23 24 Delta S, Nm 1.94 1.94 1.92

The data in Table 20 show that the fiber particle according to the invention does not show an effect on delta torque values.

TABLE 21 Evaluation of treated fibers for improvement in mechanical properties Experiment G 23 24 Modulus, 300%, MPa 14.4 15.5 15 Hardness (IRHD) 73 72 72

It is clear from the data depicted in Table 21 that the peroxide containing fiber particles (mix 23 and 24) of the invention have similar modulus and hardness as the reference compound.

TABLE 22 Evaluation of improvement in dynamic mechanical properties Experiment G 23 24 Heat build-up, ° C. 28.6 28.1 27.6 Loss modulus, MPa 1.467 1.334 1.279 Tangent delta 0.163 0.152 0.149

It is noted that the peroxide containing fiber particles (mixes 23 and 24) show improved dynamic mechanical properties, especially about 8% decrease in tangent delta.

TABLE 23 Evaluation of treated fiber particle in Payne effect at 100° C. Experiment G 23 24 Δ(G′_(0.7)-G′₂₀) (kPa) 269 226 215 Δ(G′_(0.7)-G′₉₀) (kPa) 324 280 267

It is noted that the peroxide containing fiber particles (mixes 23 and 24) show improved Payne effect indicating a better distribution of carbon black in the rubber.

EXAMPLE 5

The same particle was applied as in Example 2.

Details of the formulations of this example are given in Table 24.

TABLE 24 Experiment Ingredients H 25 Keltan ® 578 100 100 FEF - N550 60 60 SRF - N765 40 40 Sunpar ® 2280 50 50 Rhenogran ® ZMMBI-50 1.5 1.5 Naugard ® 445 1.5 1.5 sulfur 0.3 0.3 Perkadox ®14-40 Kpd 9 9 T11 0 2 Keltan ® 578 is an EPDM compound; Sunpar ®2280 is a paraffin processing oil; Rhenogran ® ZMMBI-50 is 50 wt % polymer bound methyl-2-mercaptobenzimidazol; Naugard ® 445 is 4,4′-bis(α,α-dimethylbenzyl)diphenylamine; Perkadox ® 14-40 K-pd is 40 wt % di(tert-butylperoxyisopropyl)benzene on clay.

The vulcanized rubbers listed in Table 24 were tested according to ASTM/ISO norms. A is a control experiment (rubber only), and 1 is an experiment according to the invention. The results are given in Tables 25 to 27.

TABLE 25 Effect of the mixes at 100° C. on processing characteristics (Mooney viscosity). Experiment H 25 ML(1 + 4), MU 58.9 64.1

The data of Table 25 show that the staple fiber particle according to the invention show low viscosity as evidenced from the ML (1+4) values.

TABLE 26 Effect of the mixes at 150° C. on delta torque. Experiment H 25 Δ(G′_(0.3)-G′₂₀) (kPa) 229 177 Δ(G′_(0.3)-G′₉₀) (kPa) 278 236

It is noted that the peroxide containing fiber particle (mix 25) shows improved Payne effect indicating a better distribution of carbon black in the EPDM.

TABLE 27 Evaluation of improvement in dynamic mechanical properties Experiment H 25 Loss modulus, MPa 1.164 1.056 Tangent delta 0.174 0.153

It is noted that the peroxide containing fiber particle (mix 25) show improved dynamic mechanical properties, especially a 12% decrease in tangent delta.

EXAMPLE 6

Staple fiber pellets were prepared according to WO 00/58064 and contained 80 Wt % of fiber as indicated in Table 28 and 20 wt % polyethylene resin, The treatment of the pellets was done in the following way:

About 50 g of para-aramid pellets were mixed with molten wax containing a radical initiator in order to obtain an active oxygen concentration of about 1% unless indicated otherwise. Subsequently, pellets were cooled using dry-ice and a small excess of solidified wax, possibly containing small amounts of radical initiator, was removed by sieving. The p-aramid fiber pellets are summarized in Table 28. In addition, Silenka 3 mm short cut glass fiber was treated with wax and peroxide in a similar fashion.

TABLE 28 Fiber-matrix-radical initiator particles. Particle:polymer:wax radical initiator:additive wt %:wt %:wt %:wt % Remark Entry Polyester:PE:St. St.: 39.7:9.9:37.7:12.8 invention T20 Trigonox29-C75 Polyester:PE:St. St. 39.3:9.9:50.8 comparison T21 Nylon:PE:St. St.: 38.8:9.7:38.5:13.0 invention T22 Trigonox29-C75 Nylon:PE:St. St. 38.5:9.6:51.9 comparison T23 Lyocell:PE:St. St.: 39.4:9.9:37.9:12.8 invention T24 Trigonox29-C75 Lyocell:PE:St. St. 39.0:9.7:51.3 comparison T25 Silenka:St. St.: 34.6:48.9:16.5 invention T26 Trigonox29-C75 Silenka:St. St. 34.3:65.7 comparison T27 Twaron:PE:St. St.: 39.3:9.9:38.0:12.8 invention T28 Trigonox29-C75 Twaron:PE:St. St. 42.9:10.7:46.4 comparison T29 PE = polyethylene; St. St. = stearyl stearate (Radia ® 7501 from Oleon NV); Lyocell is cellulose yarn; Silenka = Silenka 3 mm PPG ECG Tex Z20.

The accelerator employed was N-cyclohexyl-2-benzothiazole sulfenamide (CBS). Details of the formulations are listed in Table 29.

TABLE 29 Rubber formulations incorporating aramid fiber particles Experiment Ingredients J K 26 27 28 29 30 31 32 33 34 35 NR SVR 10 80 80 80 80 80 80 80 80 80 80 80 80 Europrene BR 40 20 20 20 20 20 20 20 20 20 20 20 20 Black N-326 55 53 53 53 53 53 53 53 53 53 53 53 Zinc oxide 5 5 5 5 5 5 5 5 5 5 5 5 Stearic acid 2 2 2 2 2 2 2 2 2 2 2 2 Aromatic oil 8 8 8 8 8 8 8 8 8 8 8 8 Antidegradant 6PPD 2 2 2 2 2 2 2 2 2 2 2 2 Antioxidant TMQ 1 1 1 1 1 1 1 1 1 1 1 1 Sunolite 240 2 2 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 Accelerator CBS 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 T20 0 0 3 0 0 0 0 0 0 0 0 0 T21 0 0 0 3 0 0 0 0 0 0 0 0 T22 0 0 0 0 3 0 0 0 0 0 0 0 T23 0 0 0 0 0 3 0 0 0 0 0 0 T24 0 0 0 0 0 0 3 0 0 0 0 0 T25 0 0 0 0 0 0 0 3 0 0 0 0 T26 0 0 0 0 0 0 0 0 3 0 0 0 T27 0 0 0 0 0 0 0 0 0 3 0 0 T28 0 0 0 0 0 0 0 0 0 0 3 0 T29 0 0 0 0 0 0 0 0 0 0 0 3 NR is natural rubber; BR is polybutadiene; 6PPD is N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine; TMQ is polymerized 2,2,4-trimethyl-1,2-dihydroquinoline antioxidant; CBS is N-cyclohexyl benzothiazyl sulfenamide.

The vulcanized rubbers listed in Table 29 were tested according to ASTM/ISO norms. J and K are control experiments (rubber only), 27, 29, 31, 33, and 35 are comparison experiments (fiber with matrix and/or wax without peroxide) and 26, 28, 30, 32, and 34 are experiments according to the invention. The results are given in Tables 30-32.

TABLE 30 Effect of the mixes at 150° C. on delta torque. Experiment J K 26 27 28 29 30 31 32 33 34 35 Delta S, Nm 1.59 1.53 1.46 1.51 1.45 1.54 1.46 1.55 1.42 1.52 1.49 1.58

The data in Table 30 show that the particles according to the invention (mix 26, 28, 30, 32 and 34) do not influence the extent of crosslinking as demonstrated by delta S values.

TABLE 31 Evaluation of improvement in dynamic mechanical properties Experiment J K 26 27 28 29 30 31 32 33 34 35 Loss modulus, MPa 0.96 0.79 0.58 0.80 0.55 0.86 0.58 0.88 0.55 0.89 0.54 0.88 Tangent delta 0.155 0.137 0.102 0.134 0.117 0.147 0.108 0.148 0.106 0.154 0.102 0.151

The data in Table 31 show that all fiber-matrix-Trigonox 29 particles, each containing a different fiber, give a decrease in tan delta (mix 26, 28, 30, 32 and 34), whereas tangent delta is at the same level of the control experiments for the fiber-matrix particles that do not contain Trigonox 29.

TABLE 32 Evaluation of treated fiber particle in Payne effect at 100° C. Experiment J K 26 27 28 29 30 31 32 33 34 35 Δ(G′_(0.7)-G′₂₀) (kPa) 180 146 86 151 74 172 68 154 52 145 84 159 Δ(G′_(0.7)-G′₉₀) (kPa) 222 193 134 200 121 221 108 194 90 184 128 200

It is noted that the all fiber-matrix-radical initiator particles (mix 26, 28, 30, 32 and 34) show improved Payne effect indicating a better distribution of carbon black in the rubber irrespective of the fiber type, whereas the Payne effect is at the same level of the control experiments for the fiber-matrix particles that do not contain a radical initiator.

EXAMPLE 7

Staple fiber pellets Were prepared according to WO 00/58064 and contained 80 wt % of Twaron and 20 wt % of resin as indicated in Table 33. The treatment of the pellets was done in the following way:

About 50 g of para-aramid pellets were mixed with molten wax containing a radical initiator in order to obtain an active oxygen concentration of about 1% unless indicated otherwise. Subsequently, pellets were cooled using dry-ice and a small excess of solidified wax, possibly containing small amounts of radical initiator, was removed by sieving. The p-aramid fiber pellet particles are summarized in Table 33. In addition Twaron pulp was treated with wax and peroxide in a similar fashion.

TABLE 33 Fiber-matrix-radical initiator particles. Particle:polymer:wax: radical initiator wt %:wt %:wt %:wt % Remark Entry Tw pulp:—:St. St.: 34.4:—:49.9:15.7 invention T30 Trigonox 29-C75 Twaron:PA:St. St.: 35.2:8.8:28.0:28.0 invention T31 Trigonox 29-40B Twaron:PP:St. St.: 37.0:9.3:26.9:26.8 invention T32 Trigonox 29-40B Tw pulp = Twaron 1093 pulp; PA = polyamide; PP = polypropylene; St. St. = stearyl stearate (Radia ® 7501 from Oleon NV).

The accelerator employed was N-cyclohexyl-2-benzothiazole sulfenamide (CBS). Details of the formulations are listed in Table 34.

TABLE 34 Rubber formulations incorporating aramid fiber particles Experiment Ingredients L M 36 37 38 NR SVR 10 80 80 80 80 80 Europrene BR 40 20 20 20 20 20 Black N-326 55 53 53 53 53 Zinc oxide 5 5 5 5 5 Stearic acid 2 2 2 2 2 Aromatic oil 8 8 8 8 8 Antidegradant 6PPD 2 2 2 2 2 Antioxidant TMQ 1 1 1 1 1 Sunolite 240 2 2 1.1 1.1 1.1 Accelerator CBS 1.5 1.5 1.5 1.5 1.5 sulfur 1.5 1.5 1.5 1.5 1.5 T30 0 0 3 0 0 T31 0 0 0 3 0 T32 0 0 0 0 3 NR is natural rubber; BR is polybutadiene; 6PPD is N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine, TMQ is polymerized 2,2,4-trimethyl-1,2-dihydroquinoline antioxidant, Sunolite 240 is a microcrystalline wax, CBS is N-cyclohexyl benzothiazyl sulfenamide.

The vulcanized rubbers listed in Table 34 were tested according to ASTM/ISO norms. L and M are control experiments (rubber only), and 36 to 38 are experiments according to the invention. The results are given in Tables 36-37.

TABLE 35 Effect of the mixes at 150° C. on delta torque. Experiment L M 36 37 38 Delta S, Nm 1.52 1.51 1.43 1.45 1.46

The data in Table 35 show that the particles according to the invention (mix 36 to 38) do not influence the extent of crosslinking as demonstrated by delta S values,

TABLE 36 Evaluation of improvement in dynamic mechanical properties Experiment L M 36 37 38 Loss modulus, MPa 0.89 0.82 0.47 0.52 0.49 Tangent delta 0.148 0.143 0.093 0.099 0.096

The data in Table 36 show that most particle-matrix-Trigonox 29 compositions, comprising different particles, both chemically and physically, and different matrices, give a decrease in tan delta (mixes 36 to 38).

TABLE 37 Evaluation of treated fiber particle in Payne effect at 100° C. Experiment L M 36 37 38 Δ(G′_(0.7)-G′₂₀) (kPa) 159 138 64 65 60 Δ(G′_(0.7)-G′₉₀) (kPa) 205 183 107 106 103

It is noted that the all particle-matrix-radical initiator particles (mix 36 to 38) show improved Payne effect indicating a better distribution of carbon black in the rubber irrespective of the particle type, and matrix. 

1. A particle comprising a composition containing a matrix and a peroxide or azo radical initiator wherein the particle is a fiber or fibrid selected from aramid, polyester, polyamide, cellulose, and glass.
 2. The particle of claim 1 wherein the radical initiator is a peroxide.
 3. The particle of claim 2 wherein the radical initiator is a dialkyl peroxyketal, a dialkyl peroxide, a di(alkylperoxy)alkylene, a di(alkylperoxy)aralkylene, or a mixture thereof.
 4. The particle of claim 3 wherein the radical initiator is 1,1-(tert-butylperoxy)-cyclohexane and/or 1,1-(tert-butylperoxy)-3,3,5-trimethylcyclohexane.
 5. The particle of claim 1 wherein the composition comprises 5-98 wt % of the radical initiator, based on the weight of the composition.
 6. The particle of claim 1 wherein the matrix is selected from an extrudable polymer, a wax, and a mixture thereof.
 7. The particle of claim 6 wherein the extrudable polymer is a polyolefin selected from polyethylene and/or a derivative thereof, polypropylene and/or a derivative thereof, and a mixture thereof.
 8. The particle of claim 6 wherein the wax is a saturated alkanecarboxylic acid ester having 12-50 carbon atoms, or a synthetic microcrystalline wax having a C22-C38 alkyl chain.
 9. The particle of claim 8 comprising up to 85 wt % based on the weight of the particle at least one of stearyl stearate and palmityl stearate.
 10. The particle of claim 1 wherein the particle is a poly(p-phenylene-terephthalamide) or a co-poly-(paraphenylene/3,4′-oxydiphenylene terephthalamide) fiber.
 11. The particle of claim 1 wherein the particle is a continuous fiber, chopped fiber, staple fiber or pulp, optionally which is pre-treated with a sizing.
 12. The particle of claim 1 wherein the composition amounts 5-90 wt %, based on the weight of the particle.
 13. The particle of claim 1 wherein the particle is at least partially coated with the composition.
 14. An uncured particle-elastomer composition comprising: (a) 100 parts by weight of at least one natural or synthetic rubber; and (b) 0.1 to 20 parts.
 15. A cured particle-elastomer composition obtained by curing the composition of claim 14 with 0.1 to 25 parts by weight of an amount of sulfur and/or a sulfur donor, to provide the equivalent of 0.1 to 25 parts by weight of sulfur, or 0.1 to 20 parts by weight of a peroxide.
 16. A skim product comprising the particle-elastomer composition of claim 15 and a skim additive.
 17. A mechanical rubber good comprising the composition of claim
 14. 18. The mechanical rubber good of claim 17, which is selected from a tire, a tire tread, an undertread, a belt, and a hose.
 19. A method for vulcanizing a rubber composition by vulcanizing synthetic or natural rubber in the presence of the particle of claim 1 and a vulcanization agent selected from sulfur, a sulfur donor, and a peroxide. 